This invention relates to containers in general and, specifically, to lined containers wherein the inner liner may be sealed separately and independently of the container itself. Such containers are most often utilized in the packaging of solid and liquid food products or the like, but have use in other areas as well. In the food industry, liners are also utilized as barriers to prevent undesirable chemical interaction between the container material and the container contents. Of course, containers of the type described may be employed wherever it is desired to seal the contents against air and moisture, or to prevent leakage from within, such as in the health care, pharmaceutical and other industrial packaging markets.
In the past, containers incorporating separately closable and/or removable liners have involved costly and time consuming production, particularly since a multi-step manufacturing process has been required. For example, in U.S. Pat. No. 3,321,070, a package for a liquid coating material is disclosed which contains a separately closable inner plastic film liner or bag which is separately formed and later inserted into the container. Two-step manufacturing processes and subsequent assembly steps are typical in the manufacture of containers of this type, as may be seen, for example, in U.S. Pat. Nos. 4,065,049; 3,648,882; 3,101,839; 3,055,568; and 2,920,967.
It is, of course, also well known to coextrude multi-layer bags and containers as shown in U.S. Pat. Nos. 3,896,991; 4,064,302; 4,151,318, 4,303,710; and 4,357,191. In each instance, however, the multiple layers are bonded together, thus precluding separation of an inner liner to faciliitate separate and independent closure of the liner.
It is further known in the prior art to form multi-layer bags which contain fully or partially attached liners, wherein sheet material for the various layers is continuously processed through a number of workstations where the multi-layered web is folded, glued, cut, etc. to form a finished container. Exemplary of such processes are U.S. Pat. Nos. 3,929,275 and 3,269,643.
In the present invention, a process is disclosed for forming a separable laminate container in a far simpler and less costly process than has heretofore been possible. According to this invention, at least two layers of non-adhering thermoplastic material are coextruded to form a multi-layered, tubular parison which is subsequently blow molded to the desired container shape. After trimming, a container body is produced which includes a thin film plastic liner which may be easily pulled away from the container body side walls to the extent required to roll down, fold, or otherwise seal, as by heat sealing, the open end of the liner.
In one exemplary embodiment of the invention, the outer layer which will form the container body is extruded at a thickness which, after blow molding, will be in the range of about 10 to about 50 mil. The inner layer which will form the container liner is extruded at a thickness which, after blow molding, will be in the range of about 0.5 to about 10 mil and, preferably about 0.5 to 3 mil. The thicknesses of the respective layers are chosen such that the container body will be stable, or self-supporting, while the liner will be non-self-supporting. In this regard, thicknesses up to 10 mil are generally characterized as non-self-supporting thin film material, while thicknesses above 10 mil are generally regarded as self-supporting.
After coextrusion, the multi-layer tubular parison is blow molded to form a container blank of desired shape, which may be round, rectangular, square and so on. In a subsequent step, at a nearby workstation or, as later explained, while the container is still in the mold, a tapered upper portion of the blow molded container blank is removed by cutting, thereby creating an open end of the same diameter or profile as the remainder of the container body.
If the cutting tool is adjusted to cut both layers of material, the inner liner will be axially coextensive with the outer container wall. If it is desirable to provide additional liner material to further facilitate folding, rolling down, etc., then the knife may be adjusted to penetrate the outer layer only. Subsequently, the inner liner, which now extends beyond the outer container wall, may be trimmed as desired.
After filling, the inner liner may be separated from the outer container merely by pulling the liner radially inwardly at the open end to separate it from the interior side wall surfaces of the container. The free end of the liner may thereafter be closed in any number of ways. For example, it may be gathered and tied, flattened and folded or rolled down, heat sealed, etc. If desired, a container lid may threafter be applied to the open end of the container.
As described further herein, a number of plastic materials may be employed to form the laminates. It is important, of course that no adhesives be added to the plastic material compositions in order to preclude bonding of the laminates. On the other hand, separating agents may be employed, if necessary or desired, to assure separation.
It is therefore the principal object of this invention to provide a process for simple and efficient manufacture of containers with linings or layers which may be separately closed, without any need for separate fabrication and subsequent assembly operations typically found in the prior art. Other objects and advantages will become apparent from the detailed disclosure which follows.